1. Field of the Invention
The invention relates to thermoplastic molding compositions and more particularly to autoclave resistant molding compositions which are blends of poly(ester-carbonate) and polyetherimide or poly(ether sulfone) resins.
2. Brief Description of the Related Art
Poly(ester-carbonate) (PEC) resins have been useful as ingredients in the preparation of blends of thermoplastic molding resins. These blends can be attractive to mold particular articles having certain desirable physical properties. For example, U.S. Pat. No. 4,430,484 (Quinn) issued Feb. 7, 1984, describes blends of poly(ester-carbonate) resins with aromatic polyamides, polyimides, polyamideimides and polyetherimides showing improved properties, such as higher heat distortion temperature under load. However, articles molded from some of these blends can exhibit some brittleness and blistering when subjected to autoclave conditions typical for sterilization of medical equipment.
In copending and commonly owned U.S. patent application Ser. No. 716,940, filed Jun. 18, 1991, now abandoned, ternary blends of polyetherimides, siloxane polyetherimide copolymers and polycarbonate resins including poly(ester-carbonate) resins are described broadly as thermoplastically moldable to obtain ductile articles with improved flame retardancy and strength properties useful in engineering thermoplastics.
In copending and commonly owned U.S. patent application Ser. No. 965,484, filed Oct. 23, 1992, blends of polyetherimides and siloxane polyetherimide copolymers and polycarbonate resins including poly(ester-carbonate) resins are described broadly as a method for improving the stress crack resistance of articles.
In copending and commonly owned U.S. patent application Ser. No. 965,646, filed Oct. 23, 1992, now U.S. Pat. No. 5,387,639 ternary blends of polyetherimides, thermoplastic aromatic polyarylate resins and polycarbonate resins including poly(ester-carbonate) resins are described broadly as thermoplastically moldable to obtain ductile articles.
Many of these same blends would be useful for the manufacture of articles, such as surgical trays, for the medical industry except for the stringent and harsh sterilization conditions required for this industry. Useful articles made from these compositions for the medical industry would have to be able to withstand autoclave sterilization at temperatures of at least 270.degree. F. for as many as 500 cycles without deforming or blistering while maintaining their physical properties. Additionally, these compositions would have to be sufficiently ductile to avoid cracking and breakage from routine handling, including dropping. Although poly(ester-carbonate) resins have the impact strength needed for these applications, they are unable to withstand the autoclave sterilization procedure. Conversely, polyetherimide resins can withstand the autoclave sterilization procedure but are too brittle to meet the toughness requirement. Thus, there is a long felt need for the development of ductile compositions that are able to withstand repeated autoclave sterilization conditions without distorting or blistering.